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This book introduces aqueous geochemistry applied to geothermal systems. It is specifically designed for readers first entering into the world of geothermal energy from a variety of scientific and engineering backgrounds, and consequently is not intended to be the last word on geothermal chemistry. Instead it is intended to provide readers with sufficient background knowledge to permit them to subsequently understand more complex texts and scientific papers on geothermal energy. The book is structured into two parts. The first explains how geothermal fluids and their associated chemistry evolve, and shows how the chemistry of these fluids can be used to, deduce information about the resource. The second part concentrates on survey techniques explaining how these should be performed and the procedures which need to be adopted to ensure reliable sampling and analytical data are obtained. A geothermal system requires a heat source and a fluid which transfers the heat towards the surface. The fluid could be molten rock (magma) or water. This book concentrates on the chemistry of the water, or hydrothermal, systems. Consequently, magma-energy systems are not considered. Hot-dry rock (HDR) systems are similarly outside the scope of this text, principally because they contain no indigenous fluid for study. Both magma-energy and HDR systems have potential as energy sources but await technological developments before they can be exploited commercially. Geothermal systems based on water, however, are proven energy resources which have been successfully developed throughout the world.

Geothermal Fluids: Chemistry and Exploration Techniques

I Geothermal Fluid Chemistry.- 1 Geothermal Systems.- 1.1 System Types and Characteristics.- Classification.- 1.2 Genesis of Geothermal Fluids.- Origin of water and solutes.- Evolution of geothermal fluids.- Evolution of steam: boiling point-depth relations.- Age of geothermal fluids and geothermal systems.- 1.3 Thermal, Hydrological and Chemical Structure.- Liquid-dominated systems.- Vapour-dominated systems.- 2 Water Chemistry.- 2.1 Water Types.- Chloride.- Sulphate.- Bicarbonate.- Sulphate-chloride.- Dilute chloride-(bicarbonate).- A diagnostic plot of water chemistry.- 2.2 Processes Affecting Water Composition.- Mineral-fluid equilibria.- Boiling (adiabatic) cooling.- Conductive cooling.- Mixing (dilution) with other waters.- 2.3 Interpretation of Water Chemistry.- pH.- Common solutes.- Chemical behaviour of common species.- Chemical indicators of physico-chemical processes.- Statistical analysis of water chemistry.- 2.4 Mixing Models.- Enthalpy - Chloride diagrams.- Enthalpy - silica diagrams.- Carbonate - silica/chloride.- 2.5 Solute Geothermometers.- Silica.- Na/K geothermometer.- Na-K-Ca geothermometer.- Na/Li geothermometer.- K/Mg and Li/Mg geothermometers.- Na-K-Mg geothermometer.- Ca/Mg gt; SO4/F geothermometers for carbonate reservoirs.- 2.6 Calculattng Reservoir Fluid Chemistry.- Heat and mass balance equation.- Steam fraction calculation.- Weirbox composition.- Reservoir fluid composition.- Total discharge (TD) composition.- Reservoir fluid pH.- 3 Gas Chemistry.- 3.1 Introduction.- 3.2 Discharge Features.- 3.3 Processes Affecting Steam Composition.- Geothermal system.- Solubility.- Steam formation.- Condensation.- Oxidation.- Rock-steam reactions.- Mineral equilibria and buffering.- Seismicity.- Contamination.- 3.4 Interpretation of Gas Chemistry.- Behaviour of common geothermal gases.- Indicators of physico-chemical processes.- 3.5 Gas Geothermometers.- CO2-H2S-H2-CH4 geothermometer (D'Amore gt; Panichi).- CO-based geothermometer.- CO2-geothermometer.- H2 Ar geothermometer.- gas/?water - based geothermometers.- 4 Isotope Chemistry.- 4.1 Introduction.- Notation.- Standards.- 4.2 Geothermal Applications of Isotopes.- Stable isotope.- Radioactive isotopes.- 4.3 Isotope Geothermometers.- Isotope geothermometry equations.- Oxygen isotope geothermometers.- Hydrogen isotope geothermometers.- Carbon isotope geothermometers.- Sulphur isotope geothermometer.- II Exploration Techniques gt; Surveys.- 5 Exploration Techniques.- 5.1 Introduction.- 5.2 Exploration Surveys.- Active systems.- Fossil/epithermal systems.- 6 Water Surveys.- 6.1 Pre-Field Laboratory Preparation.- Collection bottles.- Bottie cleaning.- Sampling equipment.- 6.2 Field Survey.- Mapping springs.- Field notes.- Field measurements.- Selection and prioritizing springs for sampling.- 6.3 Sampling Methods.- Springs and pools.- Wells.- Specialised sampling requirements.- Sample storage.- 6.4 Analytical Methods.- Aluminium.- Ammonia.- Arsenic.- Bicarbonate, Carbonate.- Boron.- Caesium.- Calcium.- Chloride.- Fluoride.- Hydrogen sulphide.- Iodide, Bromide.- Iron.- Lithium.- Magnesium.- Mercury.- pH.- Potassium.- Rubidium.- Silica.- Sodium.- Sulphate.- Total Dissolved Solids.- 6.5 Data Quality and Presentation.- Quality control checks.- Ionic balance.- Mass balance.- Units.- Tabulation of results.- 7 Gas Surveys.- 7.1 Pre-Field Laboratory Preparation.- Sample flasks.- Flask cleaning and preparation.- Sampling equipment.- 7.2 Field Survey.- Selection and prioritizing fumaroles for sampling.- 7.3 Sampling Methods.- Fumaroles.- Gas discharges from pools.- Wells.- General notes on sampling gases Sample storage.- Sample storage.- 7.4 Analytical Methods.- Gas chromatographic determinations.- Wet chemical determinations.- Calculation of gas in the total discharge (TDgas).- 7.5 Gas Concentration Units.- 8 Soil and Soil-Gas Surveys.- 8.1 Introduction.- 8.2 Survey Organisation.- Orientation survey.- Sampling grid.- 8.3 Soil Surveys.- Soil sampling.- Sample preparation.-